The leaching of heavy metal bearing wastes and human and biological exposure to heavy metal content has long been of concern to environmental regulators and waste producers. Under the Resource Conservation and Recovery Act (RCRA) solid waste is classified by the U.S. Environmental Protection Agency (EPA) as hazardous waste if excessive amounts of heavy metals leach from the waste when tested under the Toxicity Characteristic Leaching Procedure (TCLP). EPA also regulates the land disposal of certain heavy metal bearing wastes depending on the content of the heavy metals regardless of the leaching potential. In addition, several state governments require solid wastes with elevated levels of heavy metals be disposed of as a hazardous waste. Disposal of waste at a hazardous waste landfill is typically more expensive than disposal at non-hazardous waste landfills.
To reduce the expenses associated with the landfill disposal of heavy metal leachable waste, particularly lead bearing waste, various methods to control heavy metal leaching and reduce heavy metals have been developed. These methods include the stabilization of lead bearing waste with, for example, portland cement, silicates, sulfates, water soluble phosphates and combinations thereof as well as acid digestion and subsequent extract metals recovery. However, these methods are often expensive to perform and involve complex handling equipment and operations. Additionally, some of these methods use chemicals, such as high molarity acids, which in the amounts used, are very corrosive to the waste generation and/or treatment process equipment. These methods also alter the nature of the waste which complicates the ability of the waste to be further processed. These methods also use water soluble chemicals which, upon additional wet processing of the waste, are subject to loss due to water solution stripping.
Thus a need exists for means of reducing lead leaching from the lead bearing waste which are less expensive, less damaging to equipment and allows the waste to be further processed and handled after stabilization.